iOS and Location Services

CS4521

Core Location

• Framework to determine the current latitude and longitude of a device

• Core Location uses a type of streaming notification so that your application receives updates as the GPS ascertains a more accurate fix.

• CAREFUL: can be expensive for battery

There are three technologies that corelocation uses :

o GPS Reads microwave signals from multiple satellites to determine the current

locationo Cell Tower Triangulation Determine the current location by calculation based on location of cell

towers in iPhone’s range.o Wi-Fi positioning Service (WPS) Uses IP address from iPhone’s Wi-Fi connection by referencing database of

service providers and areas they service

Location Manager(CLLocationManager)

• create an instance of Location Manager.CLLocationManager *locationManager=[[CLLocationManager alloc]init];

• Assign a delegate object to it, and configure the desired accuracy you want.

Location Object(CLLocation)

• Represents the location data generated by a CLLocationManager object.

• Lat, Long, accuracy and when taken

CLLocationAccuracy - Setting Desired Accuracy

CONSTANTS declared in CoreLocation/CoreLocation.h (in degrading accuracy)

o kCLLocationAccuracyBesto kCLLocationAccuracyNearestTenMeterso kCLLocationAccuracyHundredMetreso kCLLocationAccuracyKilometerso kCLLocationAccuracyThreeKilometers

Setting Delegate and Accuracy:

locationManager.delegate=self;locationManager.desiredAccuracy= kCLLocationAccuracyBest

Setting Distance Filter

• you can tell Location manager not to notify for every change in location but to only notify you when location changes by certain amount.

• Setting up a distance filter reduced the amount of polling that your application does.

• Specifying a distance filter of 1000 tells location manager not to notify the delegate until the iPhone has moved at least 1000 meters from previously reported position

• For example:locationManager.distanceFilter=1000.0f;

• To return location manager to return to default setting with no filter then:

locationManager.distanceFilter= kCLDistanceFilternone;

Setting Distance Filter Example

Starting the Location Manager

• It will continue to call your delegate method whenever it senses a change that exceeds the current distance filter

[locationManager startUpdatingLocation];

Location Manager Delegate

CLLocationManagerDelegate

• defines the methods used to receive location and heading updates from a CLLocationManager object.

• YOU WILL create your OWN Location Manager Delegate class and implement methods of your need.

CLLocationManagerDelegate

Getting Location Updates

When the location manager wants to inform its delegate of the current location, it calls:[LocationMangerDelegate locationManger:lm didUpdateToLocation:tLoc fromLocation:fLoc]

locationManager:didUpdateToLocation:fromLocation

o locationManager= First parameter is location Manager that called the delegate.

o didUpdateToLocation= Second is CLLocation object that defines current location of iPhone

o didUpdateToLocation=Third parameter is CLLocation object that defines previous location from last update (will be nil if method is called first time.)

Implement the method-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation

{ //save location in class variable currentLocation self.currentLocation = newLocation;   if(newLocation.horizontalAccuracy <= 100.0f) { [locationManager stopUpdatingLocation]; }}

Getting Latitude and Longitude using CLLocation

• CLLocation object has some properties that might be interest to your application

• The latitude and longitude are stored in property called coordinate.

CLLocationDegrees latitude=theLocation.coordinate.latitude;CLLocationDegrees

longitude=theLocation.coordinate.longitude;

• CLLocation object also tell you how confident the location manager is in latitude and longitude calculations by the property horizontalAccuracy which describes the radius a circle with coordinates as its center.

Getting Latitude and Longitude using CLLocation

• The CLLocation object also has a property called altitude that tell you how many metres above the sea level you are:

CLLocationDistance altiude=theLocation.altitude

• Each CLLocation object maintains a property called verticalAccuracy that indicate how confident core location is in its altitude determination.

• If verticalAccuracy is negative core location is telling you that it cannot determine the altitude.

Getting Latitude and Longitude using CLLocation

• has timestamp • getDistanceFrom: method calculates distance

etween 2 CLLocation objects

CLLocationDistance dist; dist =[fromLocation getDistanceFrom:toLocation];

• Note: ignores the altitude as if both locations are at sea level

Error Notification

• locationManager:didFailWithError:.o Method called when can not get location of device will call

second delegate method named

• KCLErrorDenied: o first time your application goes to determine location an

alert will popup on screen asking user if its OK for the current program to access your location.

o If user clicks the Don’t Allow button,your delegate will be notified with an error code kCLErrorDenied.

• kCLErrorLocationUnnowno which indicate core location unable to determine location

but will keep trying.

Another CCLocationManagerDelegate

method –handling errors- (void)locationManager:(CLLocationManager *)manager didFailWithError:

(NSError *)error

{ if(error.code == kCLErrorDenied) { [locationManager stopUpdatingLocation]; } else if(error.code == kCLErrorLocationUnknown) { // retry } else { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error retrieving location"

message:[error description] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; }

}

Trying Out Core Location

>>>app get current location and total distance travelled while program has been running.

Step 1- create the project

• In Xcode, create a new project using view-based application template and call the project WhereAmI..

• Expand the classes and resources folders and single-click WhereAmIViewContoller..h and make following changes

Step 2- WhereAmIViewContoller..h

NOTE: your app’s ViewController IS theCLLocationMangerDelegate

NOTE: ViewController contains class variables of the CLLocationManger andCurrent CLLocation

Step 2- Create XIB using Interface

Builder1. Open WhereAmIViewController.xib in IB. Drag 6

UILabel labels from library to the view window.

2. Connect to proper outlets

Step 3-

WhereAmIViewController.m

Create this code

Get CLLocationManger and start it

Release locationManger ---save Battery!!!!

Step4: To WhereAmIViewController.h add the CLLocationManager Delegate Method to get Update

Gets Lat and Longand saves it in UILabel’s of the View

Step5: To WhereAmIViewController.h add the CLLocationManager Delegate Method to handle Errors

Applicatio

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